1. Field of the Invention
The present invention relates to a method for producing 5′-guanylic acid, and a novel microorganism used for this production. 5′-guanylic acid is useful as a food seasoning, a pharmaceutical, and in raw materials thereof.
2. Brief Description of the Related Art
Known examples of industrial methods for producing 5′-guanylic acid, also known as guanosine-5′-monophosphate, or “GMP”, include producing guanosine by fermentation and then subjecting it to enzymatic phosphorylation, to obtain 5′-guanylic acid (JP 07-231793 A, JP 10-201481 A, WO 96/37603 and JP 2001-245676 A).
Other methods of producing GMP have been reported, including culturing both an Escherichia bacterium with increased GMP synthetase activity, and a Brevibacterium ammoniagenes which is able to biosynthesize large amounts of adenosine-triphosphate (ATP) (hereinafter also referred to as the “regeneration of ATP”) and synthesize GMP from 5′-xanthylic acid (XVIP) in a culture medium containing XIVIP, and ammonia or glutamine. ATP is necessary for glucose metabolism, and XIVIP can be converted into GMP with high efficiency. In this way, GMP can be produced and accumulated in the culture (Tatsuro Fujio, et al., Biosci. Biotech. Biochem., 1997, 61(5), pp. 840-845.).
Methods to produce GMP by fermentation have also been proposed. For example, in JP 56-12438 B, a method for producing GMP is disclosed wherein a mutant strain of the genus Bacillus with adenine auxotrophy, resistance to decoyinine or methionine sulfoxide, and the ability to produce GMP is cultured, and GMP is produced and recovered from the culture medium. Furthermore, JP 2002-355087 A discloses a method for producing GMP using a strain produced by deleting two kinds of 5′-nucleotidase genes in an Escherichia bacterium having an ability to produce inosinic acid (inosinic acid-5′-monophosphate, hereinafter also referred to as “IMP”) and amplifying the IMP dehydrogenase and GMP synthetase genes. This strain is cultured, and GMP produced and recovered from the culture medium. However, in general, the yield of GMP is not sufficient in direct fermentation and therefore such methods are not practical as compared to the above-described enzyme methods.
As mentioned above, research has been conducted relating to the production of 5′-guanylic acid, and several successful examples have been reported. However, the function of the nucleotidase(s) is/are not fully understood. Several nucleotidases have been found and it is known that when deleted, the yield of 5′-guanylic acid is improved (JP 2002-355087 A and WO 2006/078132). However, it is difficult to completely inhibit degradation of the product, which can be problematic.